JimGnitecki

My C63's tire psi lable on the driver's door post clearly shows that the tire psi should be 46 psi front and 49 psi rear:




But, I keep reading about guys on this forum running 38 psi or thereabouts.

I do have the 19 inch wheels and P31 package.

Have other owners with the MB 19" wheels found that the 46F / 49R is somehow not the best?

The difference here between the 46F / 49R and what I am reading on the forum seems pretty big.

Jim G

Jasonoff

Door panel ratings are for GVWR using the OEM tire load spec. The inside of your fuel door will show 2 examples with a passenger count.

This all changes with your tire load rating though.

EDIT: Fuel door sticker example

Diabolis

^ This. Assuming that you're using OEM wheels / tire sizes, use pressures as indicated on the fuel door label.

JimGnitecki

Ok, here is the tire psi label on my fuel door:



My car has the 19" wheels from the factory.

Notice that it calls for 44 psi Front / 42 psi Rear at moderate loading.

Notice that it calls for 46 psi Front / 49 psi Rear at maximum loading.

Notice that heavier loading barely affects the front tire psi, but maximum loading necessitates 7 psi more than moderate loading.

The maximum psi is required not only for maximum loading, but also when driving at high speed.

So, an owner with the factory 19" wheels, who either frequently carries passengers or trunk cargo, or who drives at high speed, needs to keep the rear tire psi at 49 psi unless he/she is willing to adjust the tire psi each time.

But, if he/she runs the higher rear psi all the time, including when alone in the car, can we expect the following outcomes:

- More wear along the centerline of the rear tires versus along the tread edges?

- Less traction, and earlier intervention of traction control, under high throttle situations?

- How big a deal would each of these be in typical everyday usage?

Jim G

Diabolis

Hi Jim,

Unless you intend to go driving on the autobahn in Germany with four passengers and a full trunk, what I would suggest you do is put 45 psi COLD in all four corners and enjoy the ride. At least that's what I do on mine. Oh - and at 45 psi cold, the tire wear is perfectly even.

MB_SD

IMO, with as much as -2.5 degrees of camber in the rear there is no way for even tire wear regardless of psi

Sick AF

I'll have to give this a try...
I have been running 38F/35R on 18" Conti DWS 235/255

Previous owner must have had the car repainted, and they did not put back the tire psi labels. Missing from both spots; the door jam and gas panel.

Dogtag114

I have been running 38-39 on all corners for years on 18" PSSs... I found higher pressures just created more wear in the center of the thread... this is my daily driver, no track time...

JimGnitecki

I took your advice Diablois. It makes sense given my conservative driving, moderate loading, and relatively low speeds - it's hard to go over 120kph = 72 mph on Vancouver Island without risking a big ticket and insurance hike (The Government of British Columbia has a monopoly on car insurance and uses it to punish drivers who speed).

BY the way, I am running Nitrogen in the tires (to reduce psi loss over time), as I have learned via both cars and motorcycles that the pressure loss, and also pressure variance with changing temperatures, is notably reduced.

I still cannot get over 46 psi and the super low tire profile. The high pressure, low profile (which means less overall tire carcass to absorb hits and heat), the stretched load rating, and relatively narrow tires, coupled with a high torque and high rpm engine, and the high toe-in prescribed by MB, must surely be the reasons for the really short tire life all the tire threads mention.

Jim G

Alex.currie44

Jim, you are over thinking this. As others have said follow the guidelines of the fuel door and you will not go too far wrong. Jasonoff's observations are good too recognizing he is running 18s so he has a different wall height to our 19s. If it is usually you and the misses the pressure shown work just fine and you have nothing to be concerned about re centre wear under the odd different conditions of loading. If you are going to load 4 bodies and a trunk full of luggage then maybe take them up to the next setting.
You need to worry about alignment more than tire pressures if you are worried about tire wear.
It is a basic known fact in any car what the consequences are of under inflated and over inflated tires.
On all of my 11 MB cars I have followed to fuel door or manual pressures and the only worry I had on my W124s without LSD was I tended to wear out the RR faster than the others.
If GAIN offers you an opportunity to take your car to the VIMP they will require you to run 4psi higher than the base pressures.

Diabolis

Sick AF and Dogtag114 - the 18" wheels call for lower pressures than the 19" as you have more sidewall. With 18" summers you should be running 40 psi F and maybe 42 psi R.

MB SD - I am not sure what the factory rear camber spec calls for on the C63, but both my winters, summers and track tires are wearing out evenly across the tire tread surface. Do you have any suspension mods?

Alex.currie44

When I got my car in September I had it aligned so these are specs off the results sheet they provided after alignment

Camber Front Cross Camber Front

-1.39 to -2.11 -0.40 to 0.40

Caster

Looks like 11 degrees Cross Caster -0.50 to 0.50

Toe Front

0.10 to 0.27 Total Toe 0.20 to 0.54

Camber Rear

-1.48 to -2.48

Toe Rear 0.01 to 0.25 Total Toe 0.14 0.38

Thrust Angle -.012 to 0.12

FYI

JimGnitecki

I have the 19" wheels remember, not 18", and the door pillar tag suggests 46 psi front and 49 psi rear, but as others pointed out above, that is really only needed when the car is carrying "maximum load". The fuel filler door tag suggests psi as low as 41.

After adjusting my tire psi, in all 4 tires to 46 psi, and running that way for a couple of days, I realized that the ride is not dramatically, but notably, softened from the 46 front / 49 rear I had been running. The difference is enough that I no longer "notice" the sharper pavement bumps like I did befor.

Thanks to all who chimed in on this thread.

Jim G

Alex.currie44

Mine are 19s too and the door pillar says the same thing but if you notice those high pressures are for Z rated tires at Extra load which can be interpreted as Max weight.
The 45 F and 44 R on the gas filler is 3 people and luggage. The assumption is that with the weight of the 156 engine a bit more pressure in the front is a good thing.
At 5 people and luggage you go to the higher pressure.
At 46 on all corners and since you like detail take some random depth measurements inside outside and center on your tires front and rear and see after a month or two at 46 psi what the changes are. I don't expect much but if I was to look for something I would look at centre wear in the rears.
In this car my ride on my 18 winters was noticebly softer at the same pressures. Wall height counts.